This application proposes to develop an innovative intervention that promotes physical activity to 14-17 year olds and assess its feasibility. The intervention is guided by Self Determination Theory and seeks to enhance adolescents'feelings of autonomy, competence, and relatedness, and ultimately, internally-driven motivation to be physically active, thereby increasing the likelihood of sustainable increases in physical activity. Increasing physical activity in a manner that will be sustained will ultimately decrease risk of both obesity and certain cancers. PUBLIC HEALTH RELEVANCE: This application will test the feasibility of promoting PA to 14-17 year olds using text messages tailored to constructs from Self Determination Theory. Promoting PA to adolescents in a manner that is familiar, convenient, and acceptable has the potential to increase PA, thus reducing risk of both obesity and chronic disease, such as certain cancers.